Highly repetitive low-coherence interferometry with time-stretch technique

Masaharu Hoshikawa; Katsuhiro Ishii; Takeshi Makino; Takahiro Hashimoto; Hideaki Furukawa; Naoya Wada

doi:10.1117/12.2525939

21 June 2019 Highly repetitive low-coherence interferometry with time-stretch technique

Masaharu Hoshikawa, Katsuhiro Ishii, Takeshi Makino, Takahiro Hashimoto, Hideaki Furukawa, Naoya Wada

Proceedings Volume 11056, Optical Measurement Systems for Industrial Inspection XI; 1105644 (2019) https://doi.org/10.1117/12.2525939
Event: SPIE Optical Metrology, 2019, Munich, Germany

Abstract

We construct highly repetitive low-coherence interferometer using time-stretch technique and confirm its basic characteristics. The experimental system consists of a mode-locked laser diode (MLLD), a time-stretcher, an optical interferometer, a photodiode (PD), and a real-time oscilloscope. The ultra-short pulse from MLLD was passed through a dispersion flat fiber to generate supercontinuum light with 23.5 nm wavelength bandwidth. Repetition frequency of the laser pulse is set to be 10 MHz by the LiNbO3 modulator, and then it feeds to a time-stretcher composed of a dispersion compensation fiber (DCF) with a wavelength dispersion of 8959 ps². The pulse width after passing through the timestretcher is 28.2 ns. The fiber-optic Michelson interferometer consists of a 50:50 optical fiber coupler, two collimating lenses, an objective lens and two reflective mirrors. Interference signals are detected by a photodiode (32 GHz) and recorded by a real-time oscilloscope (16 GHz, 50 GS/s). The temporal profile of the recorded interference signal is converted to an optical frequency profile. The optical path length difference is determined by Fourier transform of the spectrum. We demonstrate a preliminary measurement on the experimental system. The calculated path length difference agrees well with the actual set values. It is confirmed that the optical path length difference can be measured at a high repetition rate of 10 MHz. It is shown that the degradation of the interference signal can be prevented by considering the second order of the group delay of the DCF.

Citation Download Citation

Masaharu Hoshikawa, Katsuhiro Ishii, Takeshi Makino, Takahiro Hashimoto, Hideaki Furukawa, and Naoya Wada "Highly repetitive low-coherence interferometry with time-stretch technique", Proc. SPIE 11056, Optical Measurement Systems for Industrial Inspection XI, 1105644 (21 June 2019); https://doi.org/10.1117/12.2525939

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